Add test-custom-ca-bundle fips job

What does this MR do?

Add test-custom-ca-bundle fips job to check that FIPS images support custom CA certs.

gitlab-org/gitlab#355544 (comment 905460101)

What are the relevant issue numbers?

gitlab-org/gitlab#355544 (closed)

Does this MR meet the acceptance criteria?

• Tests added for this feature/bug

Tested via gitlab-org/security-products/analyzers/gemnasium!291 (closed)

• pipeline: https://gitlab.com/gitlab-org/security-products/analyzers/gemnasium/-/pipelines/512071375
• job that tests the main tmp image: https://gitlab.com/gitlab-org/security-products/tests/custom-ca/-/jobs/2308853574#L238
• job that tests the -fips tmp image: https://gitlab.com/gitlab-org/security-products/tests/custom-ca/-/jobs/2308853587#L238